File Permissions & Ownership

Linux is a multi-user operating system, so it needs a strong permission system to control who can access what.
File permissions and ownership define security, access control, and system stability.

In this blog, we will learn:

• How Linux permissions work

• What rwx means

• How ownership is managed

• Common commands with examples

Understanding File Permissions

Run:

ls -l

Example output:

-rwxr-xr-- 1 user group 1234 file.sh

Permission Breakdown :

-rwxr-xr--
│ │  │  │
│ │  │  └─ Others
│ │  └──── Group
│ └──────── Owner
└────────── File type

Permission Types (rwx)

Permission Categories

Numeric Permissions (chmod)

Numeric permissions use octal values.

Example :

chmod 755 script.sh

Explanation:

Owner: 7 (rwx)
Group: 5 (r-x)
Others: 5 (r-x)

Symbolic Permissions

chmod u+x file.sh
chmod g-w file.sh
chmod o+r file.sh

Where:

• u = user

• g = group

• o = others

• a = all

Ownership in Linux

In Linux, every file and directory has an owner. Ownership controls who can access, modify, or execute a file.

📌 Owner

• Usually the user who created the file

📌 Group

• Used to share files among users

Types of Ownership

Each file has two ownership levels:

1️⃣ User (Owner)

• The user who created the file

• Has the most control over the file

Example:

-rw-r--r-- 1 apurv devops file.txt

Here:

• apurv → Owner

2️⃣ Group

• A group of users who share access

• Useful for team collaboration

Example:

-rw-r--r-- 1 apurv devops file.txt

Here:

• devops → Group

Why Ownership Matters

Ownership decides:

• Who can read the file

• Who can modify it

• Who can execute it

Without correct ownership:

• You may see Permission denied

• Applications may fail

• Scripts may not run

Checking Ownership

Use:

ls -l

Output:

-rwxr-xr-- 1 user group script.sh

Changing Ownership

Change owner

chown user file.txt

Change owner and group

chown user:group file.txt

Change only group

chgrp group file.txt

Ownership vs Permissions (Simple Difference)

Real-Life Example

Imagine a shared project folder:

• Owner → Project lead

• Group → Team members

• Others → No access

This prevents accidental changes and improves security.

🔚 Conclusion

File permissions and ownership are fundamental to Linux security.
Understanding them helps prevent:

• Unauthorized access

• Accidental system damage

• Security breaches